This invention relates in general to sizing textile yarns, and relates in particular to an improved method and apparatus for prewetting yarns by applying a liquid spray to the yarn.
Size is applied to yarn to improve properties of the yarn prior to a weaving process. The primary properties of yarn improved by sizing are hairiness, breaking strength, resistance to abrasion, and lubrication. Sizing material typically consists of natural starches, synthetic polymers, and blends of the two with minor ingredients added.
It is known in the art that the sizing process for many types of yarn can be improved by wetting the yarn, e.g., with water, before applying size to the yarn. Prewetting the yarn removes oils and waxes from the yarn resulting in improved pickup of size when the yarn sheet, comprising a number of yarns aligned in substantially parallel relation, subsequently passes to a size bath in a vat known as a size box. The prewetting liquid also fills the central core of the yarn, displacing size that would otherwise fill the core in the subsequent application of size, so that the size is instead applied mainly to the surface of the yarn. Prewetting the yarn before applying size thus yields a significant reduction in the amount of sizing material required to size the yarn, and may also result in improved weaveability of the sized yarn. The nature of sizing processes and the resulting benefits are well known to those skilled in the art.
Yarn prewetting according to the prior art takes place by immersing the moving sheet of yarns in a prewet immersion box and then removing excess water by passing the yarn sheet through a squeeze roller assembly. The prewet immersion box and squeeze roller assembly are located a short distance upstream from the size box, so that the prewetted yarn sheet enters the size box after leaving the squeeze roller assembly. There the yarn sheet is immersed in a size bath and excess size is removed by a separate squeeze roller assembly. The construction and operation of such Prewetting apparatus and sizing apparatus are well-known in the art and need not be further detailed herein.
Stated in general terms, prewetting according to the present invention is accomplished by replacing the traditional immersion box-squeeze roll applicator with one or more liquid spray nozzles wetting the yarn prior to entry into the size applicator. The rate of prewet liquid applied to the yarn is determined by the rate of liquid flow through the spray nozzle. Retention of liquid sprayed onto the yarn may be enhanced by increasing the dwell time of the moving yarn between the prewet spray and immersion of the yarn in the size solution, so as to adjust the extent to which the Prewetting liquid penetrates the yarn before the size is applied.
Stated in somewhat greater detail, the amount of dwell time between applying the liquid spray and immersing the yarn in the size solution is adjusted, without increasing or reducing the forward speed of the yarn, by increasing or decreasing the distance between the liquid spray application and the immersion of the yarn in the size solution. In particular detail, this selective variation in distance is accomplished by passing the prewetted yarn over an adjustable roll, known as a sky roll, positioned on the yarn path between the prewet spray applicator and the size applicator. Moving the position of the sky roll thus increases or decreases that path, producing a corresponding change in the dwell time of the prewet yarn of the yarn speed itself.
The amount of liquid spray applied to the moving yarn may be adjusted without changing the forward speed of the yarn sheet. This adjustment allows applying a substantially constant predetermined amount of prewet liquid to the yarn, irrespective of changes in the forward speed of movement of the yarn through the prewet spray and the subsequent size applicator. In this manner, yarn prewetting can be preset by an operator, based on various parameters such as yarn size, the number of strands, and the amount of water pickup desired, and the amount of liquid spray applied to the moving yarn is thereafter automatically maintained independent of subsequent increases or decreases in the speed of the moving yarn sheet.
The amount of liquid spray being applied to the yarn may also be adjusted in response to the concentration of liquid size being applied to the prewetted yarn. This adjustment may be manual, or may be automated in response to the size concentration.
Accordingly, it is an object of the present invention to provide an improved method and apparatus for prewetting yarn.
It is another object of the present invention to provide an improved method and apparatus for prewetting yarn prior to applying size to the yarn.
It is a further object of the present invention to provide a method and apparatus for prewetting yarn without immersing the yarn in liquid.
It is still another object of the present invention to provide a method and apparatus for prewetting yarn with a substantially constant predetermined amount of liquid while varying the throughput of the yarn.
It is still a further object of the present invention to provide an improved method and apparatus for prewetting yarn to a selectively variable extent independently of throughput speed of the yarn.
The foregoing and other objects and advantages of the present invention will become more readily apparent from the following description of a preferred embodiment.